This invention relates generally to processes and apparatus for drying, and more particularly, to drying processes and apparatus in which a drying fluid is dehumidified and recirculated.
In most drying processes a volatile liquid is driven off from an article of interest by providing the article with sufficient heat to vaporize the liquid. This heat is often provided by a drying fluid such as hot air circulated into contact with the article in a drying chamber. The resulting vaporized liquid is admixed with the drying fluid and is exhausted from the drying chamber. Because of design simplicity as well as the historically low cost of energy the effluent mixture of drying fluid and vapor has typically been simply vented to the atmosphere. A residential clothes dryer is an example of this approach. However, such an approach inefficiently utilizes the heat of evaporation supplied to the system.
More specifically, most of the heat of evaporation supplied to a drying process may be recovered as latent heat by condensing the vaporized liquid before it is exhausted from the system. In certain applications, such as in the drying of wood, the use of a vapor compression heat pump in a drying process has been suggested to enable the recovery of available latent heat. In such a system latent heat is recovered from vaporized fluid exhausted from a drying chamber by condensation on a heat pump evaporator. The recovered latent heat is then transferred at the heat pump condenser to drying fluid entering the drying chamber.
Although drying processes involving heat pumps enable the recovery of latent heat, the use of such processes is effectively limited in scope. For example, the high capital costs associated with heat pump-coupled dryers render them unacceptable for many applications. Similarly, heat pump-coupled dryers are often susceptible to heat exchanger fouling such as in certain clothes drying applications.
Accordingly, it is an object of the present invention to provide a new and improved process and apparatus for drying.
It is another object of the present invention to provide a new and improved process and apparatus for drying in which latent heat of vaporization is efficiently recovered.
It is still another object of the present invention to provide an efficient low cost drying process and apparatus which obviates the need for heat exchangers and is adaptable to a wide range of applications.